Xander takes a sample from the Eastern Coven before they leave.

On Xander's way back to Steiner's he stops and takes a sample of what seems like the main water source in town.

Once Tarith and Dantie return to Steiner's home, Xander asks what happened at the Rose Garden. After being filled in.
A shame I missed it, would have been a sight to see. I have been comparing the water samples I have with one I gathered in Swans Rest while on my way back. Unfortunately Tarith's friends do not allow as much quite study as I had hoped and have hoped.

While Tarith and Dantie are answering the door. Xander simply looks up from his work. Upon noticing it is Jacob at the door.
Ah Jacob, I was just thinking about coming to find you, are you here to have the discussion you spoke of before we left?

Spoiler
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Xander casts detect magic while studying the 4 different samples. (font of life, swans rest, east and west covens.)

Spellcraft (1d20+21)[39]

Knowledge (Arcana) (1d20+21)[37]

Knowledge (The Planes) (1d20+15)[26] (trying to link the special properties of the water to similar special properties of water from other planes he knows of.)

Knowledge (Nature) (1d20+15)[18]